This invention relates to radiant heaters which are fueled by liquefied petroleum gas (LPG). More particularly, the invention relates to a radiant heater which is equipped with an improved burner assembly and an improved support assembly for mounting the heater on a propane tank.
Radiant heaters, sometimes called infrared heaters, which are powered by LPG such as propane, butane, isobutane and mixtures thereof are well known. For example, U.S. Pat. Nos. 4,782,814, 4,624,241, and 4,569,329 describe such radiant heaters. The heaters described in those patents are specifically designed for use with relatively small disposable LPG fuel tanks, which contains, for example, about 12 ounces of fuel.
Other radiant heaters are designed for use with larger refillable LPG tanks which can hold 20 pounds or more of fuel. Radiant heaters which are designed for use with refillable LPG tanks are generally mounted directly on the tank, for example, by connecting the fuel tube of the heater to the standard POL outlet valve of the tank.
Radiant heaters used with large, refillable LPG tanks generally provide more heat output than heaters which are used with smaller, disposable LPG tanks. However, even though the larger tanks have a substantial fuel capacity, the heat output of radiant burners has heretofore been limited. Heat output of radiant heaters is conventionally measured by the amount of fuel which is consumed by the heater in terms of Btu's per hour. The rating of prior heaters is generally limited to about 12,000 to 15,000 Btu's per hour.
The burner assembly of a radiant heater conventionally includes a burner tube for conveying a mixture of fuel and air, a porous burner head on the outlet end of the burner tube, a burner pan which surrounds the burner head, and an outer screen which extends across the burner pan. The burning fuel/air mixture heats the screen on the burner pan, and heat radiating from the burner head heats the adjacent environment.
It is desirable to confine the flame of the fuel/air mixture in the space between the porous burner head and the outer screen. It is also desirable to avoid excessively heating the outer screen which might cause the screen to deteriorate or burn away, thereby requiring replacement. However, the flame should be hot enough to provide the desired radiant heat and to provide substantially complete combustion in order to reduce the amount of unburned and partially burned hydrocarbons which are emitted from the heater.
The flow of the fuel/air mixture into the burner assembly creates noise which is clearly audible, particularly when the heater is being operated at maximum output. It is also desirable to maintain the noise at an acceptable level.
The foregoing design requirements have heretofore limited the heat output of LPG radiant heaters to about 12,000 to 15,000 Btu's per hour per burner assembly. Higher heat output was available only by using multiple burner assemblies.
The dimensions of the outer screen are generally maintained relatively small so that the screen can be heated substantially uniformly without excessive hot spots and to reduce emissions of partially burned hydracarbons. However, limiting the size of the screen also limits the heat output.
The screens on the burner pan and the burner head are subject to deterioration over time and require replacement. Generally, the higher the heat output, the more frequently the screens need to be replaced. In many heaters replacement of the burner pan screen or burner head screen is a time-consuming and laborious task.
Replacement of the screens is further complicated if the heater is equipped with a thermocouple sensor or an electronic ignition system. Many heaters have a thermocouple sensor mounted near the burner head in order to shut off the flow of fuel if the flame goes out. An electronic ignition system facilitates lighting the heater and includes a piezoelectric electrode adjacent the burner head. Replacement of the burner head often requires disassembly of the thermocouple sensor and the electrode.
A radiant heater which is designed for use with refillable LPG tanks is generally mounted on and supported by the tank. Many heaters are supported solely by a rigid fuel tube which is part of the heater and which is connected to the fuel outlet valve of the tank. However, such a connection imposes stress on the valve connection at the tank.